A group of enzymes with different substrate specificity and referred to in general as matrix metalloproteinases (hereinafter referred to as "MMPs") contributes to degradation of the extracellular matrix comprising such complex components as collagen, proteoglycan, elastin, fibronectin, and laminin.
Previously reported MMPs include interstitial collagenase (MMP-1), 72 kDa gelatinase (also known as type IV collagenase or gelatinase A; MMP-2), 92 kDa gelatinase (also known as type IV collagenase or gelatinase B; MMP-9), stromelysin-1 (MMP-3), matrilysin (MMP-7), neutrophil collagenase (MMP-8), stromelysin-2 (MMP10) and stromelysin-3 (MMP-11).
These MMPs are a family of enzymes whose primary structure has been reported previously. With the exception of MMP-7, the primary structure among the family of reported MMPs comprises essentially an N-terminal propeptide domain, a Zn.sup.+ binding catalytic domain and a C-terminal hemopexin-like domain. In MMP-7 there is no hemopexin-like domain. MMP-2 and MMP-9 contain an additional gelatin-binding domain. In addition, a proline-rich domain highly homologous to a type V collagen .alpha.2 chain is inserted in MMP9 between the Zn.sup.+ binding catalytic domain and the C-terminal hemopexin-like domain.
In highly metastatic tumour cells, there are reports of conspicuous expression of type IV collagenase (MMP-2, MMP-9) which mainly degrade type IV collagen (Cancer Res., 46:1-7, 1986; Biochem. Biophys. Res. Commun., 154:832-838, 1988; Cancer, 71:1368-1383, 1993). Likewise, it has been reported MMP-3 act as an activator of proMMP-9 (J. Biol. Chem., 267:3581-3584, 1992).
The degree of matrix metalloproteinase expression serves as an index to diagnosing the degree of cancer malignancy.